1. Field
The present disclosure relates to an internal combustion engine control apparatus.
2. Description of the Related Art
As a conventional method for estimating this type of air-fuel ratio, for example, one disclosed in Japanese Patent No. 4803100 is known. The estimation method is intended to estimate and evaluate an air-fuel ratio via a specific-heat ratio with a focus on the fact that a change in the status of an air-fuel mixture in the compression stroke in an internal combustion engine is a polytropic change and the fact that a specific-heat ratio of an air-fuel mixture varies with an air-fuel ratio. More specifically, a specific-heat ratio κ of an air-fuel mixture is calculated from respective cylinder pressures P1 and P2 detected at two predetermined crank angles θ1 and θ2 by a cylinder pressure sensor during the combustion stroke and cylinder volumes V1 and V2 corresponding to the crank angles θ1 and θ2 by the following expression:κ=log(P1/P2)/log(V2/V1)
A reference specific-heat ratio κ0 is calculated by searching across a predetermined target air-fuel ratio-specific-heat ratio map in accordance with a target air-fuel ratio set at the time. If a deviation Δκ of the calculated specific-heat ratio κ from the reference specific-heat ratio κ0 is larger than a predetermined value, a departure of an actual air-fuel ratio from the target air-fuel ratio is considered large, and ignition timing and a fuel injection quantity are corrected in accordance with the deviation Δκ.